//:C05:Box1.cpp
// Defines template operations.
#include <iostream>
using namespace std;

// Forward declarations
template<class T> class Box;
template<class T>
Box<T> operator+(const Box<T>&, const Box<T>&);

template<class T>
ostream& operator<<(ostream&, const Box<T>&);

template<class T> class Box
{
    T t;
    public:
        Box(const T& theT) : t(theT){}
        friend Box operator+<>(const Box<T>&, const Box<T>&);
        friend ostream& operator<< <>(ostream&, const Box<T>&);
};

template<class T>
Box<T> operator+(const Box<T>& b1, const Box<T>& b2)
{
    return Box<T>(b1.t + b2.t);
}

template<class T>
ostream& operator<<(ostream& os, const Box<T>& b)
{
    return os << '[' << b.t << ']'; 
}

int main(void)
{
    Box<int> b1(1), b2(2);
    cout << b1 + b2 << endl;    // [3]
    // cout << b1 + 2 << endl;   // No implicit conversions!
}